The present invention claims priority under xc2xa7119 to European Patent Application EP99109895.5 filed May 20, 1999.
The invention relates generally to wheels for automotive vehicles and more specifically to a wheel incorporating sound-absorbing material which rests on the wheel rim to reduce noise to the passenger compartment.
Tire noise is generated by resonance in the air-filled cavity between the wheel rim and the tire. Attempts to eliminate stressful noise to which passengers in the passenger compartment are subjected, by means of sound-proofing measures on the bodywork, have not led to the desired result. Attempts to avoid the formation of cavity resonances per se have likewise not achieved their aim. Thus, for example, it was not possible to prevent resonance by increasing the rigidity of the wheel rim.
Attempts have also been made to prevent resonance by vulcanizing or bonding a damping band in on the inner wall of the tire. However, it has been found that a reduction in stressful noise cannot be achieved in this way either. To reduce noise radiation from tires, EP-0 029 120 B1 has proposed to secure sound-absorbing materials on the tire beads or on the wheel rim and have them project into the interior of the tire. This is intended to a large extent to allow retrofitting to existing tires or elements associated with them. However, the disadvantage here is that when the sound-absorbing materials are secured on the tire beads, these must necessarily be exchanged as well when the tire is changed or, if they are secured on the wheel rim, they may easily be damaged when the tire is changed because they project into the interior of the tire.
Against this background, it is the object of the present invention to improve a wheel rim of the generic type in such a way that cavity resonance is eliminated without the sound-absorbing material being exchanged when a tire is changed or being exposed to the risk of damage.
According to the invention, this object is achieved in the case of a wheel rim of the type stated at the outset by virtue of the fact that a recessed receptacle for the sound-absorbing material is formed in the circumferential surface, and the radially outward side of the surface-forming structure coincides with the nominal shape of the circumferential surface.
It has been found that substantial elimination of resonance in the cavity between the tire and the wheel rim is achieved with the arrangement according to the invention of the sound-absorbing material in a depression in the circumferential surface of the wheel rim. It is not necessary for this purpose that the sound-absorbing material should project into the interior of the tire. The width of the receptacle can be 5 cm and its depth about 2 cm, for example. Since, according to the invention, the upper side of a surface-forming structure arranged above the sound-absorbing material reestablishes the actual nominal shape of the wheel rim, the space which is also available in the case of wheel rims known from the prior art, without the arrangement of sound-absorbing material, is available for the application of the tool for a tire change, with the result that the sound-absorbing material is protected from damage by the tool.
In a preferred embodiment of the invention, the receptacle runs continuously around the wheel rim. This embodiment is particularly suitable for steel rims of sheet-metal construction, for example, since only one additional rolling operation is necessary to form the receptacle during manufacture.
The surface-forming structure is preferably a perforated cover which extends continuously in the circumferential direction. This ensures maximum protection for the sound-absorbing material.
As an alternative, however, it is also possible for the surface-forming structure to be designed as ribs which are arranged at a distance from one another in the circumferential direction and extend transversely to the circumferential direction. By means of these measures, the maximum possible free surface of the sound-absorbing material is obtained in order to expose as large a proportion as possible of the surface of the sound-absorbing material to the sound waves. In addition, this reduces consumption of material.
As a further advantageous development of the invention, the surface-forming structures are welded to the circumferential surface. If the wheel rim and the surface-forming structures are produced from steel, a secure connection between the wheel rim and the surface-forming structures can in this way be made in a simple manner. A particularly preferred method for making the connection is spot welding.
In an alternative, likewise advantageous embodiment of the invention, fixing grooves, in which the surface-forming structure is secured by means of a clip or adhesive joint, are provided on both sides of the receptacle. This method of fixing proves to be advantageous especially in the case of wheel rims and surface-forming structures made of aluminum.
In another, likewise advantageous, development of the invention, the receptacle is formed by individual accommodation chambers, and the surface-forming structure is formed by the upper sides of webs which extend transversely to the circumferential direction and separate the accommodation chambers from one another. This configuration is intended especially for forged or cast wheel rims. By means of these measures, it is possible in a simple manner to prevent the sound-absorbing material from sliding along the circumference of the wheel rim.
A thin perforated film is preferably applied to the upper side of the sound-absorbing material, the film being 0.05 mm thick. The film can be applied to the inside of the surface-forming structure, for example. The arrangement of the film increases the durability of the sound-absorbing material since local friction loads between the sound-absorbing material and the surface-forming structure are avoided.
In the case of perforated surface-forming structures and/or films, the total area of the perforation openings preferably amounts to more than 40% of the covering surface. This ensures complete elimination of resonance in all cases.